The invention relates to a device and a method for detecting overlapping objects in a transport path for flat objects, such as letters etc., whereby the transport path comprises a measurement path, in which measurement path a braking device is located by which a passing object or an object from a series of overlapping passing objects is decelerated in the measurement path.
The operation of devices of this kind is often based on causing, and then measuring or observing, changes in the total length of objects in a series of overlapping objects. This length change may either occur as a consequence of the existing properties of the transport system in question or be forced by mechanical means, such as a braking device in the form of a braking roller. The length change can be determined with photocells. This method can, however, only detect overlaps in a series of objects that overlap one another partially or if a total overlap between the measuring points changes into a partial overlap.
In the devices according to this prior art it is not possible to detect total overlaps that also remain total during the measurement, since in this case the total length of the series of overlapping objects does not change.